Enter closes wxWidgets application when wxPanel added - c++

Question

The wxWidgets hello world tutorial exhibits a strange behavior. As soon as I add a panel to the application using the following line to the MyFrame constructor:
wxPanel *panel = new wxPanel(this);
The [Return] and [Keypad Enter] keys cause the program to exit (Clean Close event detected).
Why is this? Without the wxPanel, the keys do nothing.
Here is the code with the added line:
// hworld.cpp
// Version using dynamic event routing
#include <wx/wx.h>
class MyApp : public wxApp
{
virtual bool OnInit();
};
IMPLEMENT_APP(MyApp)
class MyFrame : public wxFrame
{
public:
MyFrame(const wxString& title, const wxPoint& pos, const wxSize& size);
void OnQuit(wxCommandEvent& event);
void OnAbout(wxCommandEvent& event);
};
enum
{
ID_Quit=1,
ID_About
};
bool MyApp::OnInit()
{
MyFrame *frame = new MyFrame( _("Hello World"), wxPoint(50, 50),
wxSize(450, 350));
frame->Connect( ID_Quit, wxEVT_COMMAND_MENU_SELECTED,
(wxObjectEventFunction) &MyFrame::OnQuit );
frame->Connect( ID_About, wxEVT_COMMAND_MENU_SELECTED,
(wxObjectEventFunction) &MyFrame::OnAbout );
frame->Show(true);
SetTopWindow(frame);
return true;
}
MyFrame::MyFrame(const wxString& title, const wxPoint& pos, const wxSize& size)
: wxFrame( NULL, -1, title, pos, size )
{
wxMenuBar *menuBar = new wxMenuBar;
wxMenu *menuFile = new wxMenu;
menuFile->Append( ID_About, _("&About...") );
menuFile->AppendSeparator();
menuFile->Append( ID_Quit, _("E&xit") );
menuBar->Append(menuFile, _("&File") );
// Added line causing failure.
wxPanel *panel = new wxPanel(this);
SetMenuBar(menuBar);
CreateStatusBar();
SetStatusText( _("Welcome to wxWidgets!") );
}
void MyFrame::OnQuit(wxCommandEvent& WXUNUSED(event))
{
Close(true);
}
void MyFrame::OnAbout(wxCommandEvent& WXUNUSED(event))
{
wxMessageBox( _("wxWidgets Hello World example."),
_("About Hello World"),
wxOK|wxICON_INFORMATION, this );
}

Answer 1

It's probably crashing....
I know this already but check here: http://docs.wxwidgets.org/trunk/classwx_panel.html
It'd mention it is panels did that on purpose.
Any wxWindow can use a wxSizer, this is a thing that lays stuff out (like box sizers and stuff).
While the parent of a wxWindow is the thing it is in (unless it is top-level), it must go in a sizer inside the parent.
you want something like:
wxSizer* mySizer = new wxBoxSizer(WX_VERTICAL);
setSizer(mySizer);
wxWindow newWindow = new wxPanel(this);
mySizer->Add(newWindow,1,WX_EXPAND);
the 1 is the ratio of extra space this window will get of the total (in this case 1), in the direction of the sizer (vertically)
the expand flag means "fill up your space in the axis the sizer isn't" in this case horizontally. So it will fill up all the space the sizer gives it.
If you have a horizontal sizer (puts things across) with 2 buttons, if one has weight 1 and the other 2, the one with the 2 weight will get 2/3rds of whatever space the sizer has available but doesn't use.
Each window has a desired size, a size it wants to be at least, if we have 300px and the buttons only want 100 each, the weight 2 one will get 66px extra.
You get the idea.
My names here (WX_EXPAND) could be wrong, I used wxPython first (wx.EXPAND) then came to wxWidgets, I mainly use the IDE to get the names right.
If you are looking to learn wx, do consider wxPython.

Answer 2

It's behaving now, but it's a big of a guess as to why. The program was never crashing. I traced it in debug and the close event was being called.
This closes when [Enter] is pressed:
wxPanel *panel = new wxPanel(this);
As do all of these:
wxPanel *panel = new wxPanel(this, wxID_ANY);
wxPanel *panel = new wxPanel(this, wxID_ANY, wxDefaultPosition);
wxPanel *panel = new wxPanel(this, wxID_ANY, wxDefaultPosition, wxDefaultSize, wxTAB_TRAVERSAL);
This however doesn't close with [Enter] is pressed:
wxPanel *panel = new wxPanel(this, wxID_ANY, wxDefaultPosition, wxDefaultSize, wxEXPAND);
Nor do these close:
wxPanel *panel = new wxPanel(this, wxID_ANY, wxDefaultPosition, wxDefaultSize, wxEXPAND);
wxPanel *panel = new wxPanel(this, wxID_ANY, wxDefaultPosition, wxDefaultSize, wxCLIP_CHILDREN);
wxPanel *panel = new wxPanel(this, wxID_ANY, wxDefaultPosition, wxDefaultSize, wxEXPAND | wxCLIP_CHILDREN);
But this closes again:
wxPanel *panel = new wxPanel(this, wxID_ANY, wxDefaultPosition, wxDefaultSize, wxEXPAND | wxCLIP_CHILDREN | wxTAB_TRAVERSAL);
Apparently if wxTAB_TRAVERSAL is involved in the style (it's the default for the constructor BTW) it will propagate your [Enter] keypress to the wxFrame and click the [X] close button.
The only thing even close to a hint is a cryptic and seemingly irrelevant note in the documentation:
Tab traversal is implemented through an otherwise undocumented intermediate wxControlContainer class from which any class can derive in addition to the normal wxWindow base class. Please see wx/containr.h and wx/panel.h to find out how this is achieved.
if not all characters are being intercepted by your OnKeyDown or OnChar handler, it may be because you are using the wxTAB_TRAVERSAL style, which grabs some keypresses for use by child controls.
This is my best guess. I don't know if this is intentional behavior or a bug.